I want to make sure I'm doing this right so I have the best position before I put holes in my ceiling.

What I did to find the right spot is I moved the pj to its closest possible throw distance that will fill my screen size, with the zoom all the way back to it's largest position. Then I moved the pj back about a foot or a foot and a half, just so I could move the zoom in a little bit so that it would not be at its extreme. Is this the correct place to mount it?

That's the approach I'd probably use. Technically, some might argue that your lens will be at its optimum position closer to the middle of the zoom range, but the closer you go the more lumens you'll get. Another consideration might be placement in relation to your viewers' heads (e.g., to minimize noticing the fan noise).

Also, if your projector has a decent zoom range and lens shift, you might become interested in a wider screen (e.g., 2.35:1). In my case, I'm thinking of doing this but will need to manually zoom/shift to adjust. That would require that you place the projector in a place where you can fill both screen ratios.

Scott R--------------I'd much rather watch a great movie in B&W at 240 lines of resolution than a lousy movie in 1080p with lossless audio.

I think you got his suggestion backwards, but maybe I'm the one who is confused. At 25' I should think that you would be setting the projector's lens to the max zoom length (to shrink the image), while at the closest distance, you'd be "un-zooming" the lens. My thinking here (using camera zoom as a parallel) is that you are needing to utilize the zoom when you are farther away, and wanting to be at the widest angle setting when closest to the "subject" (in this case, the screen).

In any case, the argument in favor of positioning it as close as possible to the screen is that you get the maximum lumens, and an argument (I think) in favor of positioning it as far away as possible is that you might get a slightly sharper picture / minimize convergence issues. Again, though, someone feel free to correct me if I've misstated anything.

Scott R--------------I'd much rather watch a great movie in B&W at 240 lines of resolution than a lousy movie in 1080p with lossless audio.

I can anecdotally tell you that using less zoom (ie: making the picture smaller) provides a sharper picture and less optical issues. The more physical surface area of the lens you use, the worse it gets. Throw on a bright screen, and look at your lens while you zoom in and out, notice how much area gets lit up. At the edges of your lens, you'll lose sharpness and get more purple fringing.

I have a friend with an identical projector (7 units apart in serial number!) and his setup is further away, but using almost no zoom. His picture is much sharper than mine, which uses max zoom (I can't mount it any further back).

I think you got his suggestion backwards, but maybe I'm the one who is confused. At 25' I should think that you would be setting the projector's lens to the max zoom length (to shrink the image), while at the closest distance, you'd be "un-zooming" the lens. My thinking here (using camera zoom as a parallel) is that you are needing to utilize the zoom when you are farther away, and wanting to be at the widest angle setting when closest to the "subject" (in this case, the screen).

In any case, the argument in favor of positioning it as close as possible to the screen is that you get the maximum lumens, and an argument (I think) in favor of positioning it as far away as possible is that you might get a slightly sharper picture / minimize convergence issues. Again, though, someone feel free to correct me if I've misstated anything.

Maybe we are all confused....

I was going on this logic...that farthest back has NO ZOOM.

But I think the concept is that you DON"T want to to use Zoom, so you should ideally mount (if brightness and room) does not prevent at 0 zoom length...but no way can I do that..so I will just have to suffer.

I realize that the best option would be no zooming at all, but that would set the pj waaay back, and I would lose brightness. I'm lighting up a 130" 16:9 screen with an Epson 8700. I want to get it as close as possible to get as much brightness as I can, and using the least amount of zoom I can get away with. With the method I am trying in my first post, that brings me to about 14 feet. Just wondering if I should move back a little, or is this the best place for my situation?

If you mount it as close as possible to the screen (for your required image size) you may get some minor distortion but you'll get maximum brightness. So what I did was go about two feet back from the closest position, which is pretty much exactly what you said in the original post, so I would say you've got it right!

Throw distance doesn't have a huge effect on most projectors LENS anymore like it used to, projectors have just gotten a lot better and sharper in general. It can still affect it some though.

I would be WAY more worried about brightness than sharpness related to throw distance.

It at least partly depends on the specific projector to the sweet spot of the lens, as well as it depends on if you are using lens shift.
Generally farther back at Mid-Zoom to farthest throw is probably the sweeter spot IME, but the closer generally the better if you need the extra lumens. Mounting farther back can have some benefit to a projector's On/Off contrast (black level) depending on the projector, for some projectors even On/Off isn't really affected either.

If your image is TOO DIM at farthest throw, then the other attributes are less important anyhow IMO.